Using a dual plasma process to produce cobalt--polypyrrole catalysts for the oxygen reduction reaction in fuel cells -- part II: analysing the chemical structure of the films

The chemical structure of cobalt--polypyrrole -- produced by a dual plasma process -- is analysed by means of X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption spectroscopy (NEXAFS), X-ray diffraction (XRD), energy-dispersive X-Ray spectroscopy (EDX) and extended x-ray absorption spectroscopy (EXAFS).It is shown that only nanoparticles of a size of 3\,nm with the low temperature crystal structure of cobalt are present within the compound. Besides that, cobalt--nitrogen and carbon--oxygen structures are observed. Furthermore, more and more cobalt--nitrogen structures are produced when increasing the magnetron power. Linking the information on the chemical structure to the results about the catalytic activity of the films -- which are presented in part I of this contribution -- it is concluded that the cobalt--nitrogen structures are the probable catalytically active sites. The cobalt--nitrogen bond length is calculated as 2.09\,\AA\ and the carbon--nitrogen bond length as 1.38\,\AA.